Corrosion inhibitor



Patented Sept. 28, 1943 CORROSION INHIBITOR James Edgar Shields, NiagaraFalls, N. Y., as-

signor to Alox Corporation, New York, N. Y.,' a corporation of New York No Drawing. Application June 16, 1941, Serial No. 398,337

Claims.

This invention relates to the preparation of compositions of matter adapted for use in the prevention of corrosion of metallic containers used to confine water, alcohols, gasoline or other petroleum distillates including lubricating oils, and the like.

A principal object of the invention is the provision of water-soluble, oil-soluble and alcoholsoluble corrosion inhibitors for protecting, against the agencies of corrosion, metallic containers, composed either of aluminum or aluminum alloys or of aluminum alloys clad with aluminum, which are used for the storage of alcohol, gasoline, oil and the like in airplanes or other transportation equipment which supports its supply of motor fuel for locomotion. Another object of the invention is the provision of water-soluble, oil-soluble and alcohol-soluble compositions for the protection, against corrosive agencies, of iron or steel tanks such as are used for the storage of crude oil, refined oil, petroleum distillates and the like; e. g., where the stored liquids are contaminated with water resulting from the condensation of moisture in the atmosphere above the liquids held in such tanks. Further inventive objects include the provision of corrosion-inhibiting compositions adapted for use in the aqueous cooling systems of internal combustion engines and the like for protecting the latter from corrosion; for the protection against corrosion of auxiliary fuel units and containers proposed for the injection of aqueous alcohols into the combustion chambers of internal combustion engines; and for the protection against corrosion of any aqueous cooling system which is operated at low, ordinary or elevated temperatures.

It has been observed that metallic containers, 9. g., such as those composed of aluminum and/or its alloys, iron and/or steel, used generally for the storage of oil, petroleum distillates, lubricating oil, gasoline and the like become damaged by corrosion in relatively short periods of time. The corrosion in such cases is generally confined to the bottoms of such tanks, and is traceable to the corrosive action of water which is found in direct contact with the inner surfaces of the metallic tanks. The presence of water generally is brought about-particularly in partially filled containers-by the condensation of water vapor in the air above the stored liquids; globules of water may be formed on the cool metallic surface when the atmosphere above the liquid reaches dew point temperature, and these lobules seek the bottom areas of the containers by gravity difference between the water and the stored liquids. At points of contact between the globules of water and the metallic tank, corrosion takes place, causing pitting, grain boundary corrosion, or other types of corrosion mechanisms, and becomes so pronounced that destruction of containers is caused. This is particularly true in the case of liquids, such as oils, gasoline, distillates and the like, which are nonmiscible with water.

It also has been observed that alcohols, e. g., methyl, ethyl, propyl, iso-propyl, butyl, iso-butyl and poly hydroxyl alcohols, glycols, glycol esters, glycerol, and the like, exerta pronounced corrosive action upon metallic containers composed of iron, steel, copper, brass, bronze, aluminum and its alloys, metals plated with dissimilar metals, and the like. -In the case of alcohols or like substances which maybe employed, either in substantially pure form or diluted with water, as anti-freeze solutions in cooling systems of internal combustion engines, the corrosive action becomes so pronounced that it results in the destruction of the system. The type of corrosion in such cases is of varied mechanisms, the rate of, which increases with elevated temperatures, and the resulting products are of such a nature and extent as partially, or completely, to clog the passages of the cooling system, resulting in decreased efficiency and often times complete non-use ofthe system.

It also has been observed that metallic containers, such as those composed of brass, copper, bronze, aluminum, aluminum alloys, iron, steel and the like, used for the confinement of alcohols (either substantially-pure or diluted with water) It has been observed, also, that surgicalv instruments, such as those composed of steel, its

alloys, plated steel, and non-ferrous metals, cor-- rode when kept in solutions possessingantiseptic properties. Such antiseptic solutions" usually consist of a mixture of formalin-alcohol and 15% water approximately. The amount of formaldehyde present usually is found to be8 to 10% by volume.

It has been observed that mild cold rolled steel of the compositionshown for SAE 1020, and steel alloys, when submerged in water corrode in a relatively short period of time. Tools such as agitators, forked instruments, ploughs, cutters and the like composed-of iron or steel which are required to operate continuously in'contact with water or water soaked mashes, pulps and the like, corrode at a -very rapid rate, resulting in hydrocarbons under controlled procedures, in the liquid phase, by the Burwell process. For economical purposes, commercially available fractions of petroleum such as, kerosene, '36-40 petroleum distillate, and waxes, are chosen as starting materials for the preparation of oxidized products from which various mixtures of carboxylic acids of different molecular weights and boiling ranges may be obtained. For instance, should it be desired to obtain carboxylic acids ranging in molecular carbon from C4 through to C23, liquid hydrocarbons ranging in Beaum gravity from 52 to 36), which hydrocarbons are available in kerosene and 36-40 petroleum distillate fractions, should be chosen as starting materials. On the other hand, should still higher molecular weight carboxylic acidsv be desired, higher molecular weight, normally solid, hydrocarbons of the waxy type are chosen. Such commercially available waxy type hydrocarbons are known as sharples wax," crude scale wax, and parafiin wax. Relatively pure carboxylic acids ranging in molecular carbon from 04 through to C33 or higher may be obtained from the oxidation products of such waxes, the major portion of the acidic component of these oxidized products consisting of higher. molecular weight acids than those obtained from oxidized normally liquid hydrocarbons. Carboxylic acids can be obtained more economically from the oxidation of normally liquid hydrocarbons such as kerosene or 36-40 petroleum distillate than from the oxidation of higher molecular weight normally solid hydrocarbona such as petroleum waxes.

Amine salts obtained by reacting amines .with carboxylic acids derived from the oxldized'prodnets of kerosene, fuel oil and petroleum waxes are all efiective corrosioninhibitors'to a varying degree. Those obtainedufrom reacting. amines with the lower molecular weight carboxylic acids obtained from the oxidized products of kerosene, in general are more effective as cor rosion inhibitors thamthose derived from reacting the amines withpetroleum acids from the oxidized products of sharples wax or crude scale wax.

The methods and procedures of partially oxidizing kerosene or 36-409. petroleum distillate, and the procedure in the fir'ststep of separating saponifiable products from those which do not saponify readily in strong caustic, are given in U. S. Patents Nos.v 1,690,768and 1,690,769 to Arthur W. Burwell. The research disclosed and claimed herein relates in part to the method of recovery of carboxylic acids in substantially pure state from the saponifiable oxygenated products, The soda soapsof the carboxylic acids in the saponifiable mass of the oxidized products of kerosene or 36-40 petroleum distillate are completely hydrolyzed by strong mineral acids (e. g., hydrochloric or sulphuric acid) and the resulting mixture of carboxylic acids, occluded non-acidic oxygenated products and unattacked hydrocarbons is washed with water until free from mineral acids. It has been found that the saponifiable portion of the partially oxidized products of kerosene or 36-40 petroleum distillate when produced on a large scale includes admixtures of such oxygenated products as ketones, alcohols and small amounts of unattacked original hydrocarbons with the carboxylic acids. This. mass is then distilled in a stream of relatively dry steam to a final temperature of 550 to 600 F. by

application of external heat. Measurement of the temperature is made in the residual mass and notin the vapors. The distillation process is so designed that the current of dry steam is conducted to the bottom of the still and there released so, as to pass through the heated mass in order to entrain the volatile products. These volatile products (including water vapor) are condensed and received in a vessel suitable for the separation of the water-insoluble products. The water which contains soluble acids is continually drawn off leaving a light colored distillate of agreeable odor consisting mostly of volatile carboxylic acids, ketones, alcohols, esters,

lactones and unattacked hydrocarbons. This distillate is then digested under atmospheric pressure with strong caustic soda (5 normal) for several hoursin order completely. to saponify' natant layer forming a clear, light colored, agreeable smelling, non-aqueous solution. The aque ous soap solution is drawn off free from the unsaponifiable layer and completely hydrolyzed by strong hydrochloric acid. The so-separated acids are washed sufiiciently to remove all traces of mineral acid, and the entrained water permitted to separate by allowing the acids to remain at a slightly elevated temperature for some time. Acids recovered in this manner are clear but usually have a dark wine color. In order to obtain acids of better color, the separated acids are-distilled under reduced pressure, resulting in a recovery of about 93 to 99% of relatively light colored pure acids with an agreeable odor.

The neutralization number of acids recovered, by the process just described, from partially oxidized 36-40" petroleum distillate by the Burwell method was found to average 330 -(mgs.of KOH per l gram of acid).- This value was arlived at by averaging a number of results obtained on acids recovered from various lots of oxidized ,36-40 petroleum distillate. The distillate was obtained from a given source but oxidized at various times. The extremes of the values were found to be between 310 and 350 (mgs. of KOH per gram of acid). This average neutralization number, namely 330, appears to be typical of this particular group of petroleum acids and may be used as a means of partially identifying them.

It was found that the average saponification number of this group of petroleum acids,'afterdigesting at boiling temperature in strong alcoholic potassium hydroxide was 390 mgs. of KO-I-Ij I This value is the average per 1 gram of acids. of determinations made on a number of recovcries and may be deemed typical of this particular group of petroleum acids. The difference between the neutralization number and the total:

saponification number of this group denotes they. presence,in small amounts, of other sap'oniflable' compounds than the carboxylic groups. These may be esters, lactones, traces of keto-alcohols, or the like. V

An average fractional distillation at atmospheric pressure of these petroleum acids was found to be as follows:

C. Initial boiling point -1- 1'10 Decomposition point---" 270 Both acid and saponiflcation numbers were determined on equal fractions taken as follows, during the distillation of a certain lot of these petroleum acids:

Fraction No. Amount Distillation temperature Distilled between 170 and 210 C. Distilled between 210-215" C. Distilled between 215-220 C. Distilled between 220-224 C. Distilled between 224-228" C. Distilled between 228235 C. Distilled between 23524l G. Distilled between 24l267 C. Distilled between 267270 C.

ssenc s assseesss l Distillate flowed steadily between ZOO-210 C.

Fraction No. Add N From the neutralization numbers thus found of the petroleum acids derived from oxidized 36-40 petroleum distillate by the Burwell process, the mean molecular weight of the acids was calculated as follows:

M=molecular weight in grams.

N=grams of KQH found to neutralize 1 gram of acid.

The amount pl KOH found to neutralize 1 gram of the mixed acids was .033 gram therefore:

or 170 mean molecular weight. When this mixture of purified petroleum acids was completely reacted with mono-N-amylamine (90% monoamylamine content) it was found that the weight ratio was 1 part acid to -.56 part 'mono-N-amylamine, This reaction is given as follows (where R represents the aliphatic radical of the carboxylic acid): i

Molecular relation to the mean molecular weight of the petroleum acid is as follows:

mono-N-amylamine to 1 part petroleum acid.

The actual amount of commercial mono-N- amylamine, 90% content, used completely to react with the acids was found to be .560 part to 1 part of acid. Correcting for the amine content in the commercial product the ratio is 1 part of. acid to .504 mono-N-amylamine. This ratio checks very closely with the theoretical; namely, 1 part acid to .511 part mono-N-amylamine which tends to substantiate the mean molecular weight value calculated from the neutralization number.

When commercial N-cyclo-hexyl-amine was reacted to complete neutralization with these petroleum acids, it was found that the combining ratio by weight was 1 part acid to .595 part N-cyclo-hexyl-amine. The cyclo-hexyl amine content of the commercial product was found to be approximately This reaction may be exemplified as:

Molecular weight relation to the mean molecular weight of the acids is as follows:

99:170=.582 part N-cyclo hexylamine to 1 part petroleum acidt It will again be observed that the ratio of commercial N-cyclo hexylamine to petroleum acids agrees very closely to the theoretical ratio, atter correcting for the N-cyolo-hexylamine content.

Alkyl, aralkyl, aryl, and cyclo-paraffinic amines react in the same manner with these petroleum acids as described above to form salts. The resail-ting compounds all possess corrosion-inhibiting properties to a varying degree when used in systems consisting of metal-oil-wat'er. The

monoor primary amine salts of all groups are more potent corrosion inhibitors than are the corresponding salts of either the secondary or tertiary amines, which 'circumstancamay be accounted for by the fact that the primary amine salts are more soluble inthe phase ofthe wateroil systems than the other amine compounds. It has been found that in all groups those petroleum acid salts of amines of hydrocarbon chains containing 5 or more carbon atoms in the chain are more potent corrosion inhibitors than are those derived from amino-compounds having a lower number of carbon atoms. This might be ac-' counted for to some degree on the basis that the lower molecular weight amines are more volatile than those higher in molecular weight, and hence the loss of the inhibitor due to evaporation from the medium in which it is dissolved is greater for the lower molecular weight amine than for that of greater weight. those amine salts from amines containing hydroxyl groups have only a very poor-4f anysolubility in gasolines, petroleum distillates, lubricating oils and the like, and hence that such amine salts from hydroxyl amines have only a Very limited utility in association with th petroleum .products mentioned.

It should be noted, here, that It has also been discovered that the unseparated distillate resulting from the-steam distillation, as previously described, of partially oxidized hydrocarbons (kerosene or 36-40 petroleum distillate) when reacted with amines, particularly with mono-amylaminm possesses excellent corrosion-inhibiting properties. This product was found to be very effective in retarding the rate of corrosion of aluminum containers used for the storage of gasoline. It has been observed that containers constructed from a clad metal composed of aluminum over a core of aluminum alloy known as "17ST corrodes very rapidly in the presence of gasoline containing a small amount of added water. Cup-shaped specimens of this metal (known as "Alclad"), when partially filled with gasoline to which water was added, corroded to such an extent in 20 to 60 days as completely to destroy the container by pitting through the bottom and side walls below the liquid line. The metal walls and bottom in this case were from .35 to. .40 inch in thickness. In contrast to this, when the water-containing gasoline was treated with .5% by volume of the amine salt product resulting from the reaction of mono-amylamine with the total steam distillate of the partially oxidized hydrocarbons and placed in the same type of container no corrosion or pitting had taken place during the period of observation. Observation in this case was carried on over a period of 9 months. At the end of this time the inside surfaces of the container were as brilliant as they were at the time the test was started and free from pits and etchings.

It is known that the distillate of oxidized kerosene or 36-40 petroleum distillate recoveredby the method previously described, and referred to in the preceding paragraph, consists approximately of 40 to 60% by volume of petroleum acids, and 60 to 40% by volume of unsaponifiable bodies, known to be ketones, alcohols, esters, lactones and unoxidized hydrocarbons. Inclusion of all of these bodies with the amine salts of the petroleum acids-that is to say, use of the mixture referred to in the preceding paragraph-apparently is essentialto the long-continued prevention of corrosion of aluminum and aluminum alloys in a system of gasoline-water-metal. Thus, it has been found that when amine salts resulting from the reaction of 2-ethyl-hexyl amine (or mono-amylamine, or mono-cyclohexylamine) with substantially pure petroleum acids was used in gasoline-water mixtures, corrosion o! the container-while slowed-did take place, so that at the end of 6 to '7 months storage period destructive corrosion of the aluminum container was evidenced. 0n the other hand, it was found that when thesame volume of unsaponifiable bodies of the steam distillate were used in the gasoline-water mixture no corrosion-p inhibiting action was observed: the cup specimen used to confine this mixture corroded in the same period as did those used to confine the untreated gasoline-water mixture. No explanation can be advanced for the peculiar eflicacy of the "impure amine salts" product (that is, of the aforesaid mixture of amine salts of petroleum acids .with the commonly associated unsaponifiable bodies) asopposed .to the pure amine salts alone, and as opposed 'to the unsaponifiable bodies nevertheless, it isa fact.

Iclaim: p

1. A corrosion-inhibiting composition soluble in mineral oils including gasoline and in normally liquid alcohols of the type of ethyl alcohol, comprising a mixture of organic reaction products of an organic amine having at least 5 carbon atoms per molecule and selected from the group consisting of alkyl amines, cyclo-paraffinic amines and aryl amines, with a mixture of substantially aliphatic saturated carboxylic acids derived from a normally liquid fraction of petroleum-by liquidfined in claim 1, in which the organic amine em- 7 ployed in thereaction is 2-ethyl-hexylamine.

5. The corrosion-inhibiting composition definedinclaim 1,inwhichthemixtureofsubstantially aliphatic saturated carboxylic acids employed in the reaction has a mean molecular weight of about 170.

Mm SHIELDS.

alone: 

